The present invention relates to a process for producing L-tryptophan, L-tyrosine or L-phenylalanine, by fermentation. L-tryptophan is useful in the medical, food and animal feed industries. L-Tyrosine is useful in the medical industry. L-Phenylalanine is useful in the medical and food industries.
As the microbiological processes for producing such aromatic amino acids using a microorganism belonging to the genus Corynebacterium or Brevibacterium, the following processes have been known so far; for example, a process using a mutant strain to which amino acid auxotrophy and/or resistance to analogs of the aromatic amino acids is/are imparted (Journal of Japan Agricultural Chemistry Association, 50, (1), p.R. 79, 1976), and processes using strains in which activity of a rate limiting enzyme involved in the biosynthetic pathways for the aromatic amino acids has been amplified by the introduction of the genes coding for the rate limiting enzyme (U.S. Pat. No. 4,874,698, and European Publication No. 338,474).
It has been desired to develop a more industrially economical method for the production of L-tryptophan, L-tyrosine or L-phenylalanine.
The present inventors have found that L-tryptophan, L-tyrosine and L-phenylalanine can be produced in a higher yield by intensifying transetolase activity in the aromatic amino acid-producing microorganism belonging to the genus Corynebacterium or Brevibacterium.
Transketolase catalyzes the following two reactions in the pentose phosphate cycle. Transketolase is considered to play an important role in the synthesis or decomposition of erythrose-4-phosphate, which is the initial substrate for the biosynthesis of the aromatic amino acids.
(i) Fructose-6-phosphate+glyceraldehyde-3-phosphate .fwdarw./.rarw. erythrose-4-phosphate+xylulose-5-phosphate PA1 (ii) Ribose-5-phosphate+xylulose-5-phosphate .fwdarw./.rarw. glyceraldehyde-3-phosphate+sedoheptulose-7-phosphate